AN4092 datasheet(18/38 Pages) STMICROELECTRONICS

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Power Management Controller (PMC)

AN4092

18/38

Doc ID 023080 Rev 2

1.7.1

Internal logic power consumption

Most of the logic is powered by the 1.2V. In the worst case, the power that must be

dissipated internally is given by the maximum VDD voltage multiplied by the maximum

current required: VDDmax * IDDmax. IDDmax normally depends on the operating frequency.

1.7.2

Analog power consumption

In the worst case the power required by the ADC that must be dissipated internally is given

by the maximum VDDA voltage multiplied by the maximum current required: VDDAmax *

IDDAmax. The analog current consumption does not depend on the system operating

frequency.

1.7.3

Voltage regulator power consumption

The internal 3.3V regulator uses the 5V provided on the VDDREG to generate the 3.3V. The

same voltage is used to supply the 1.2V regulator. The worst case scenario is: VDDREGmax

* IDDREGmax. When disabled but VDDREG is still powered, there is still a small current

consumption due to the LVI circuitry and the 1.2V regulator. IDDREG does not depend on

the operating frequency.

1.7.4

3.3V power consumption

When in single supply configuration, the 3.3V is generated internally, therefore the current

consumption is already taken in account in the maximum IDDREG.

When the 3.3V is provided externally, the IDD33 current must be taken in account:

VRC33max * IDD33max. IDD33 does not depend on the operating frequency.

1.7.5

IOs power consumption

This power consumption depends on the application: pad type, load, switching frequency,

voltage and slew rate. The current consumption of the pads is specified in the device

datasheet for a given load and a given frequency. The other cases can be extracted from

the given data assuming a linear behavior. For example, in the table is shown that a slow

pad with 50pF load switching at 4MHz consumes in average 0.5mA. If in the application the

pad is switching only at 20KHz (assuming the same load), the average consumption is 0.5 *

20000 / 4000000 = 2.5uA. Assuming VDDEH = 3.3V, the power is: 3.3 * 2.5 E-6.

1.7.6

Package power dissipation

Once computed all the power requirements, given a operating temperature and package

(and PCB), it is possible to compute whether or not the power can be dissipated in the

package. The limit is the junction temperature; for this family of devices Tj = 150C.

Let’s assume that the operating temperature is Tamb = 100C and the total thermal resistance

is RθJA = 19C/W, then the maximum power that can be dissipated is (Tj - Tamb) / RθJA =

2.63W.

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